Of central importance in Lewis's discussion of natural law is his critique of the moral relativism of utilitarianism ("the end justifies the means") as a theory of ethics and guide to behavior. Lewis claimed that the precepts of moral ethics cannot just be innovated or improvised as we go along. Picking and choosing among the code of the Tao is inherently foolish and harmful. He noted, for example, that attempts to define moral ethics as the product of a physicalism of survival and instinct create a profound dilemma. On the one hand, the utilitarian (or "Innovator," as Lewis called him) tries to make judgments of the value of human choices by claiming that one decision is good or not. But on what basis is this valuation made if the only standard that exists is instinct? Lewis shows that all such valuations necessarily must use an objective standard of the Tao to do so, even if only partially. As he stated,

The Innovator . . . rates high the claims of posterity. He cannot get any valid claim for posterity out of instinct or (in the modern sense) reason. He is really deriving our duty to posterity from the Tao; our duty to do good to all men is an axiom of Practical Reason, and our duty to do good to our descendants is a clear deduction from it. But then, in every form of the Tao which has come down to us, side by side with the duty to children and descendants lies the duty to parents and ancestors. By what right do we reject one and accept the other? . . . [T]he Innovator may place economic value first. To get people fed and clothed is the great end, and in pursuit of it, scruples about justice and good faith may be set aside. The Tao of course agrees with him about the importance of getting the people fed and clothed. Unless the Innovator were himself using the Tao he could never have learned of such a duty of justice and good faith which he is ready to debunk. What is his warrant? He may be a jingoist, a racialist, an extreme nationalist, who maintains that the advancement of his own people is the object to which all else ought to yield. But no kind of factual observation and no appeal to instinct will give him a ground for this opinion. Once more, he is in fact deriving it from the Tao: a duty to our own kin, because they are our own kin, is a part of traditional morality. But side by side with it in the Tao, and limiting it, lie the inflexible demands of justice, and the rule that, in the long run, all men are our brothers (The Abolition of Man, p. 43, bold italicized in original).

Lewis hence described the natural law as a cohesive and interconnected objective standard of right behavior:

This thing which I have called for convenience the Tao, and which others may call Natural Law or Traditional Morality or the First Principles of Practical Reason or the First Platitudes, is not one among a series of possible systems of value. It is the sole source of all value judgements. If it is rejected, all values are rejected. If any value is retained, it is retained. The effort to refute it and raise a new system of value in its place is self-contradictory. There has never been, and never will be, a radically new judgement of value in the history of the world. What purport to be new systems or (as they now call them) "ideologies," all consist of fragments from the Tao itself. Arbitrarily wrenched from their context in the whole and then swollen to madness in their isolation, yet still owing to the Tao and to it alone such validity as they possess. If my duty to my parents is a superstition, then so is my duty to posterity. If justice is a superstition, then so is my duty to my country or my race. If the pursuit of scientific knowledge is a real value, then so is conjugal fidelity (The Abolition of Man, p. 44, bold italicized in original).